IP-Header
Question 1 |
For which one of the following reasons does Internet Protocol (IP) use the time-to- live (TTL) field in the IP datagram header?
Ensure packets reach destination within that time | |
Discard packets that reach later than that time | |
Prevent packets from looping indefinitely | |
Limit the time for which a packet gets queued in intermediate routers |
Question 1 Explanation:
It prevent infinite looping over network . Because each router decrease its value by one and when this (TTL) value become zero , then it is discarded by router silently.
Question 2 |
Which one of the following fields of an IP header is NOT modified by a typical IP router?
Checksum | |
Source address | |
Time to Live (TTL) | |
Length |
Question 2 Explanation:
Option C (TTL) is decremented by each visited router. When it reaches to Zero, then Packet will be discarded.
Option A (Checksum) needs to be updated by each visited Router since TTL Value is modified.
Option D (Length) also modified whenever there is a need of performing the fragmentation process.
Option B (Source Address) can’t be modified by an IP router. Only NAT can modify it.
Option A (Checksum) needs to be updated by each visited Router since TTL Value is modified.
Option D (Length) also modified whenever there is a need of performing the fragmentation process.
Option B (Source Address) can’t be modified by an IP router. Only NAT can modify it.
Question 3 |
The maximum number of IPv4 router addresses that can be listed in the record route (RR) option field of an IPv4 header is _________.
9 | |
10 | |
11 | |
12 |
Question 3 Explanation:
A record route option is used to record the internet router that handles the datagram. It can be used for debugging and management purpose.
In IPv4 header, 40 bytes are reserved for OPTIONS.
For Record Route to stores, 1 byte is used to store type of option, 1 byte for length and 1 byte for pointer. Out of 40 bytes, 37 bytes are left.
Each IP4 address takes 32 bits or 4 bytes.
Therefore, it can store at most floor (37/4) = 9 router addresses.
Hence correct answer is 9 router address.
In IPv4 header, 40 bytes are reserved for OPTIONS.
For Record Route to stores, 1 byte is used to store type of option, 1 byte for length and 1 byte for pointer. Out of 40 bytes, 37 bytes are left.
Each IP4 address takes 32 bits or 4 bytes.
Therefore, it can store at most floor (37/4) = 9 router addresses.
Hence correct answer is 9 router address.
There are 3 questions to complete.